1. Technical Field of the Invention
The present invention relates to a cleaning apparatus and an image forming apparatus and in particular, to a cleaning apparatus for cleaning a toner remaining on a photoreceptor, a transfer body, or the like and an image forming apparatus provided with that cleaning apparatus.
2. Related Art
A general electrophotographic process is carried out by steps including charging onto a photoreceptor, image exposure, development, transfer from the photoreceptor onto a material to be transferred and cleaning of a residual transfer toner remaining on the photoreceptor after the transfer, and if desired, additionally, destaticization of the photoreceptor.
In the development, when a dry electrophotographic system is concerned, an image is formed on the photoreceptor by a powdered toner, and the image is transferred onto paper or an intermediate transfer medium. On that occasion, a residual transfer toner remaining on the photoreceptor or a toner which has not been transferred from the photoreceptor due to a paper jam or the like is removed from the photoreceptor by a cleaning apparatus. As a toner removing member which is used in the cleaning apparatus, a variety of materials such as a blade, a brush to which a bias has been applied, and a roll are used. In this respect, a blade cleaning system using an elastic blade made of a polyurethane rubber, etc. is comparatively inexpensive and is suited for downsizing.
However, in the case of cleaning the toner which is a fine particle using the blade cleaning system, there are some problems to be solved. For example, when the blade is brought into strong contact with the photoreceptor for the purpose of obtaining a sufficient cleaning performance, an edge of the blade may possibly be broken, or the blade may possibly be turned up. Further, when the blade edge is broken or abraded, the cleaning performance which has been set up at the beginning is not obtained and cleaning failure is generated, whereby serious defects are generated on an image.
Then, there is taken a countermeasure for widening a margin of the cleaning condition by containing a mold release agent such as fluorocarbon resins in a surface portion of the photoreceptor which is a member to be cleaned, thereby improving mold release properties of the photoreceptor, or intermixing a lubricant such as zinc stearate in the toner, thereby reducing the friction between the cleaning blade and the photoreceptor surface and making the toner readily separate from the photoreceptor.
However, what a large amount of the mold release agent is intermixed in a photoreceptor surface material must scarify characteristics of the photoreceptor to some extent so that a high-performance photoreceptor is hardly obtained. Furthermore, what the lubricant is intermixed in the toner influences the charge performance not a little so that a high-performance toner is hardly obtained. Moreover, even when the foregoing countermeasure is taken, it is not always easy to make sufficient cleaning performance and durability compatible with each other.
Then, not only the countermeasure against the photoreceptor or toner but also a countermeasure from a material of the cleaning blade is proposed. For example, JP 2004-191708 A discloses an example in which the tear strength of a contact portion of the cleaning blade with the photoreceptor is enhanced such that the blade edge is not broken.
According to JP 2004-191708 A, it is described that by applying a coating containing a carbon nano tube in the edge portion of the cleaning blade, not only friction resistance in the contact portion with the photoreceptor is brought without affecting the elasticity as a whole of the blade, but also the tear strength of the edge portion is markedly enhanced so that the durability of the blade edge part can be tremendously enhanced. Further, there is disclosed the use of a single wall carbon nano tube containing a fullerene therein as one example of the carbon nano tube.
By using such a blade, the durability of the cleaning blade is certainly enhanced. However, in recent years, in electrophotographic apparatus, it is eagerly required to make the maintenance free or to prolong an interval of the maintenance. In the cleaning blade of the foregoing cited reference, since the coating treatment containing a carbon nano tube is applied in only the edge part, there are encountered problems such that when the blade edge is abraded, the base material layer is immediately exposed and that when in speculating it, thick coating is applied, coating unevenness is generated, or it becomes difficult to keep the precision of the blade edge part.
On the other hand, there is also proposed an approach for enhancing the cleaning performance by adjusting an angle of the edge of the cleaning blade.
For example, JP 2-216178 A disclose a technology in which the angle of the edge of the cleaning blade is reduced from about 90° which is a usual set value and set up at 85 to 90°.
Usually, a toner and others (since there is the case where in the developer, a variety of external additives are contained in the toner, these will be included and referred to as “toner and others” hereinafter) retain in slight amounts in a space which is formed between the edge of the cleaning blade and the photoreceptor surface coming into contact therewith. Filming may possibly be generated due to this retaining toner and others. The filming as referred to herein is a phenomenon in which a sticking layer is formed on the surface of the photoreceptor due to the retaining toner and others. Alternatively, there may be the case where the sticking layer itself is named as filming.
When filming is generated on the photoreceptor surface, the image quality is, as a matter of course, deteriorated. When the retention amount of the toner in the edge part increases, the probability of the generation of filming becomes high, whereas when the retention amount of the toner decreases, the probability of the generation of filming becomes low.
On the other hand, the toner and others retaining in the edge part also work to uniformly polish the photoreceptor surface and make it smooth.
According to the technology as disclosed in JP 2-216178 A, though the opportunity of the generation of filming is certainly reduced by decreasing the retention amount of the toner in the edge part, the work to achieve uniform polishing is also reduced at the same time.
On the other hand, in the case where the angle of the edge part is larger than 90°, the toner and others are liable to retain in the edge part, and an effect for polishing the surface of the member to be cleaned becomes large. For example, JP 5-19671 A discloses an example in which by utilizing this matter, the blade edge is set up at an obtuse angle to increase the retention of the toner and others, thereby polishing the photoreceptor.
This technology intends to make the edge angle of the cleaning blade obtuse, thereby increasing the retention of the toner and to further mix a polishing particle such as titanium oxide in the toner, thereby polishing the photoreceptor. According to this method, though it is certainly possible to shave the photoreceptor, the retention amount of the toner and others increases so that the amount of the toner and others which will become a cause of filming increases, too. Accordingly, under a circumstance in which so-called deposits (filming and the like) increase, a polishing ability for shaving them must be enhanced. That is, one must use these contradictory works sufficiently while balancing and stabilizing them. It is impossible to suppress the filming in a stable manner unless the polishing amount is set up at a considerably increased amount.
In the light of the above, according to the technologies as disclosed in JP 2-216178 A and JP 5-19671 A, the opportunity of the generation of filming is deteriorated if the retention amount of the toner is high; and the polishing action becomes large if the retention amount of the toner is high. Thus, it is difficult to bring a stable polishing action while suppressing the opportunity of the generation of filming.
Now, in electrophotographic apparatus in recent years, for the purpose of achieving a high image quality, it becomes frequent to use a small-sized toner having an average particle of not more than 6 μm or a toner close to a sphere. For that reason, it becomes difficult to keep a good cleaning performance.
Under such a circumstance, not only the durability of the blade cleaning but also the matter on how should the surface state of the side to be cleaned, for example, a photoreceptor and a transfer belt, be kept good becomes important more and more. For example, if the surface to be cleaned is roughly shaved by the toner or its external additives and others retaining on the cleaning blade or in the vicinity of the edge of the cleaning blade, thereby forming irregularities on the photoreceptor surface, or the toner or its external additives are stuck onto the surface, even when the durability of the cleaning blade is enhanced, it is impossible to keep good cleaning performance.